1. Field Of The Invention
The present invention relates to a resin composition. More particularly, the present invention is concerned with a resin composition comprising, in specific proportions, a copolymer comprising hexagonal units, methyl methacrylate units, (meth)acrylic acid units and optionally aromatic vinyl compound units, a graft copolymer rubber and at least one polymer selected from a polyamide and a polycarbonate. The resin composition has surprisingly improved impact strength not possessed by any of the individual component polymers of the resin composition, while maintaining advantageous properties, such as moldability, mechanical strengths, rigidity, heat resistance, moisture resistance, chemical resistance and dimensional stability, attributed to the individual component polymers. Advantageous applications of the resin composition of the present invention are found in the manufacturing of various parts for automobiles, household electrical appliances and business machines.
2. Discussion of Related Art
Polyamide resins are now widely used as parts for automobiles, household electrical appliances and business machines. Generally, polyamide resins have excellent chemical resistance, heat resistance and wear resistance. However, the shrinkage thereof at the time of molding is large so that a molded article is likely to have disadvantageous sink marks and warp. Moreover, polyamide resins exhibit high water absorption, and are likely to suffer from a marked lowering in mechanical strength and change in dimension, which are attributed to water absorption.
Various proposals have been made in order to cope with the drawbacks of the known polyamide resins. For example, it was proposed to use a resin composition comprising a polyamide and, blended therewith, a polystyrene, a styrene-acrylonitrile copolymer, etc. (see Japanese Patent Application Publication Specification No. 40-7380/1965). The polymers employed for blending have low compatibility with the polyamide so that a layer peeling (a phenomenon in which a surface portion is peeled in the form of a skin layer) is likely to occur in a molded article. The low compatibility further causes the molded article to suffer from a marked lowering in mechanical strength. Therefore, the above-mentioned resin composition has inherent drawbacks and is not satisfactory for use in the manufacturing of parts to be incorporated in automobiles, household electrical appliances and business machines.
Further, it was proposed to use a resin composition comprising a copolymer composed of styrene units and units of a five-membered ring acid anhydride, such as maleic anhydride, which copolymer has molecular chains chemically bonded to those of a polyamide [see British Patent No. 2,060,649 (corresponding to Japanese Patent Application Laid-Open Specification No. 56-50931/1981)]. The resin composition has drawbacks in that it has poor rigidity, Izod impact strength, falling weight impact strength, scuff resistance and wear resistance.
Still further, it was proposed to use a resin composition comprising a polyamide and, blended therewith, a copolymer comprising hexagonal acid anhydride units of the formula: ##STR1## wherein each of R.sup.1 and R.sup.2 is independently a hydrogen atom or a methyl group, methyl methacrylate units, aromatic vinyl compound units and (meth)acrylic acid units (see Japanese Patent Application Laid-Open Specification No. 61-89255/1986). The resin composition has a drawback in that its Izod impact strength is as poor as 3.3 to 4.3 kg.cm/cm (1/4 inch in thickness, notched).
Still further, it was proposed to use a resin composition comprising a polyamide and, blended therewith, a polyglutarimide [see European Patent No. 94,215 (corresponding to Japanese Patent Application Laid-Open Specification No. 58-208348/1983 and Japanese Patent Application Publication Specification No. 63-22229/1988)]. The Izod impact strength of the resin composition is as poor as 7.5 to 8 kg.cm/cm (1/4 inch in thickness, notched).
As described above, various resin compositions comprising a polyamide as a base component have been proposed, but all of the compositions have problems with respect to the properties required for the parts of automobiles, household electrical appliances and business machines.
Also, polycarbonate resins are now widely used as parts for automobiles, household electrical appliances and business machines. Generally, polycarbonate resins have excellent heat resistance, mechanical strength, chemical resistance and transparency. However, the resins have drawbacks in that the Izod impact strength thereof is dependent highly on the thickness of the molded product, and in that the moldability of the resins is poor.
Various proposals have been made in order to cope with the drawbacks of the polycarbonate resins. For example, it was proposed to use a resin composition comprising a polycarbonate and, blended therewith, a terpolymer of acrylonitrile, butadiene and styrene (generally known as "ABS resin"). In this connection, reference is made to Japanese Patent Application Publication Specification No. 38-15225/1963. Further, it was proposed in Japanese Patent Application Publication Specification No. 39-71/1964 to use a resin composition comprising a polycarbonate and a terpolymer of methyl methacrylate, butadiene and styrene (generally known as "MBS resin"). Still further, it was proposed in U.S. Pat. No. 4,254,232 (corresponding to Japanese Patent Application Laid-Open Specification No. 55-80459/1980) to use a resin composition comprising a polycarbonate, a polyglutarimide and an MBS resin. Of these resin compositions, the compositions comprising a polycarbonate and a resin selected from an ABS resin and an MBS resin have a drawback in that simultaneous improvement of moldability and heat resistance or rigidity is difficult. On the other hand, the resin composition comprising a polycarbonate, a polyglutarimide and an MBS resin does not have satisfactory impact strength.
As described above, various resin compositions comprising a polycarbonate as a base component have been proposed, but all of the compositions have problems with respect to the properties required for the parts of automobiles, household electrical appliances and business machines.
In Japanese Patent Application Publication Specification No. 62-25700/1987, it was proposed to use a resin composition comprising a copolymer composed of hexagonal acid anhydride units, methyl methacrylate units, aromatic vinyl compound units and (meth)acrylic acid units and a graft copolymer rubber. The resin composition has excellent moldability, tensile strength, rigidity, transparency and heat resistance. However, the resin composition has a drawback in that the impact strength thereof is poor.
As apparent from the foregoing, a number of resin compositions have been proposed for use in the manufacturing of various parts to be used in automobiles, household electrical appliances and business machines. However, all of the known resin compositions have drawbacks with respect to the properties required for such parts. Therefore, there has been a strong demand in the art for a resin composition which is excellent in all of the properties, i.e., moldability, mechanical strength, rigidity, heat resistance, moisture resistance, chemical resistance, dimensional stability and impact strength.